1. Field of the Invention
The present invention relates to a conductive copolymer, a conductive copolymer composition, a conductive copolymer composition film and an organic optoelectronic device using the same.
2. Description of the Related Art
Optoelectronic devices, e.g., organic light emitting diodes (hereinafter, referred to simply as “OLEDs”), organic solar cells and organic transistors, convert electric energy into light energy, and vice versa.
In particular, with technical developments in the field of flat panel displays (hereinafter, referred to simply as “FPDs”), OLEDs have recently attracted much attention.
Based on rapid technical development, liquid crystal displays (LCDs) have the highest market share (i.e., 80% or more) in the flat panel display products. However, large-screen (e.g., 40 inch or more) LCDs have drawbacks in terms of slow response speed, narrow viewing angle, and the like. There is a need for a novel display to overcome these drawbacks.
Under these circumstances, since organic light emission diodes have advantages of low driving voltage, self-luminescence, slimness, wide viewing angle, rapid response speed, high contrast, and low cost, they have been the focus of intense interest as the only devices capable of satisfying all requirements for next-generation FPDs.
In recent years, a great deal of research has been conducted in the field of optoelectronic devices including OLEDs in order to form a conductive copolymer film capable of favorably transporting charges (i.e., holes and electrons) created on electrodes into an optoelectronic device, and thus realizing high efficiency of the device.
When a current is applied to a thin film composed of a fluorescent or phosphorescent organic compound (hereinafter, referred to simply as an “organic film”), electrons are recombinated with holes in the organic film to emit light. OLEDs are self-luminescent devices employing such a phenomenon. To improve luminescence efficiency and lower a driving voltage, OLEDs generally have a multilayer structure including a hole injection layer, a light emission layer and an electron injection layer as organic layers, rather than a monolayer structure exclusively consisting of a light emission layer.
The multilayer structure can be simplified by leaving one multifunctional layer and omitting other layers. OLEDs may have the simplest structure including two electrodes, and a light emission layer interposed between the two electrodes. In this case, the light emission layer is an organic layer capable of performing all functions.
However, for substantial improvement in luminance of OLEDs, an electron injection layer or a hole injection layer must be introduced into a light-emission assembly.
A variety of organic compounds that transport charges (holes or electrons) are disclosed in patent publications. Materials for the organic compounds and use thereof are generally disclosed, for example, in EP Patent Publication No. 387,715, and U.S. Pat. Nos. 4,539,507, 4,720,432, and 4,769,292.
A charge transporting organic compound currently used in organic EL devices is poly(3,4-ethylenedioxythiophene)-poly(4-styrenesulfonate) (PEDOT-PSS) in the form of an aqueous solution, which is commercially available from Bayer AG under the trade name “Baytron-P”.
PEDOT-PSS is widely used in fabrication of OLEDs. For example, PEDOT-PSS is deposited on an electrode made of a material, e.g., indium tin oxide (ITO) by spin coating to form a hole injection layer. PEDOT-PSS is represented by Formula 2 below:

PEDOT-PSS has a structure in which PEDOT is doped with aqueous polyacid as an ionic complex of poly(3,4-ethylenedioxythiophene) (PEDOT) with polyacid of poly(4-styrenesulfonate) (PSS).
In the case where a conductive polymer composition comprising PEDOT-PSS is used to form a hole injection layer, PSS is deteriorated and thus dedoped due to its superior water-absorbability, or is reacted with electrons and thus decomposed, thereby releasing a material such as sulfate. The released material may be diffused into adjacent organic films, e.g., light-emitting layer. The diffusion of the material from the hole injection layer to the light-emitting layer leads to exciton quenching, thus causing deterioration in the efficiency and lifetime of OLEDs.